#include <iostream>
#include <fstream>

using namespace std;
ifstream in ("fractii.in");
ofstream out ("fractii.out");
long long  v[1000001];
int main()
{
  long long n,s;
  s = 1;
  in>>n;
  for(int i = 2 ;i <= n;i++){
    //cout<<v[i]<<" ";
    v[i] += i - 1;
    for(int j = (i<<1); j <= n ;j += i){
      v[j]-= v[i];
    }
    s += v[i] * 2;
    //cout<<v[i]<<'\n';
  }
  out<<s;
  return 0;
}